Circuit for driving a moving element

ABSTRACT

An electric circuit is disclosed for starting an output member in vibratory motion and maintaining the vibrations at a constant amplitude. A coil is electromagnetically coupled to the output member and performs both the driving and pick-up functions. The circuit includes two oppositely polarized transistors cooperating with a coupling capacitor to deliver current pulses of a relatively large pulse width to the coil to start the output member in vibratory motion. The pulse width is progressively decreased until the output member is vibrationally maintained at a constant amplitude and frequency.

United States Patent 91 Nemoto Jan. 16, I973 [54] CIRCUIT FOR DRIVING AMOVING 3,597,634 8/1971 Flaig ..318/128 x ELEMENT 3,229,225 1/1966Schimpf ..3|s 132 x [76] Inventor: Kouji Nemoto, Ninomiya-l082, OTHERPUBLICATIONS Akita-machi, Nishitoma-gun, 3

H TokyoJapan Transistor Manual 1964 General Electric Company,

pages 106-107 [22] I Filed: March 26,1970 Elementary Circuit Propertiesof Transistors, Vol. 3, [21] Appl.No.: 22,804 1966, John Wiley & Sons,Inc. New York, pages [30] ForeignApplicafion Prim-"y Dam PrimaryExaminer-Richard B. Wilkinson March 28, 1969 Japan ..44/23160 AssistantWeldon Attorney-Robert E. Burns and Emmanuel J. Lobato [52] U.S. CL.....3l8/l26, 58/23 [51] Int. Cl. ..H02k 33/00 [57] ABSTRACT [58] 27 5:15:g g g% g An electric circuit is disclosed for starting an output memberin vibratory motion and maintaining the vibrations at a constantamplitude. A coil is electromagnetically coupled to the output memberand [56] Reerences cued performs both the driving and pick-up functions.The UNITED STATES PATENTS circuit includes two oppositely polarizedtransistors cooperating with a coupling capacitor to deliver currentpulses of a relatively large pulse width to the coil 530,662 9/1970318/127 X to start the output member in vibratory motion. The 3,553,9551/1971 Keeper et aL 3|3/]27 x pulse width is progressively decreaseduntil the output 3,306,030 2/1967 Niley ..58/23 member is vibrationallymaintained at a constant am- 3,403,312 9/1968 Sparing 318/130 plitudeand frequency. 3,407,344 10/1968 Bansho ..58/23 3,365,635 1/1968 Shelley..3I8/128 1 Claim, 8 Drawing Figures CIRCUIT FOR DRIVING A MOVINGELEMENT This invention relates to a driving circuit for driving a movingelement and more specifically relates to a mechanical vibrator or motorrotor for use as a reference vibrator or oscillator for timepieces.

A variety of driving circuits are known for driving mechanicalvibrators, for example, tuning forks and balance wheels, as referencevibrators for timepieces. One such known circuit comprises an astablemultioscillator, a coil coupled as a load to the astable multioscillatorwhich combines pick-up and driving functions, and a vibrator havingattached thereto a magnet. In such a circuit, the coil coacts with themagnet to serve as a transducer and the astable multioscillator istriggered by an electric signal induced in the coil by the vibratorymotion of the vibrator to drive the vibrator. In the conventionaldriving circuit above described, the pulse width of the driving pulse iskept constant and consequently the vibrator cannot be supplied with asufficient pulse for its starting. Therefore, the vibrator is incapableof self-starting and must initially be driven by an external force. Thesame drawback applies to the type of ordinary driving circuit wherein amotor is used instead ofa mechanical vibrator; here again, the motorcannot start by itself.

The present invention eliminates the foregoing disadvantages of theexisting vibrator driving circuits and provides a new, improved drivingcircuit.

According to one aspect of the present invention, a driving circuit fora moving element is provided which comprises first and secondtransistors having opposite polarities connected such that the collectorof the first transistor is serially coupled to the base of the secondtransistor and a biasing resistor is connected between the base of thefirst transistor and a power source. Another resistor is connected tothe emitter of the first transistor and the emitters of both transistorsare capacitively coupled to each other. A coil is electromagneticallycoupled to a moving element and combines the function of driving themoving element with the function of picking up the motion of the movingelement. The coil is connected to the emitter of the second transistorand a d-c voltage source is connected to constitute a series circuitwith the resistors, capacitor and coil. Thus, the pulse of drivingcurrent that is supplied by the coil to the moving element has asufficiently large pulse width at the time of starting to effectself-starting of the moving element.

Once the moving element has started its motion, the coil picks up themotion and the electric signal thereby induced is superposed on thebase-to-emitter voltage to trigger the transistors. As the movingelement approaches a steady motion, a driving current with aprogressively decreasing pulse width is automatically developed andapplied. This results in small power consumption during the steadymotion. Also, a driving force synchronized with the motion of the movingelement is obtained.

It is an object of the present invention to provide a driving circuitcapable of self-starting the motion of the moving element and minimizingthe power consumption during the steady motion of the moving element.

Another object of the present invention is to provide a driving circuitwhich is simplified in construction, inexpensive to manufacture, andadapted for mass production.

Other features, advantages, and objects of this invention will becomeapparent from the following detailed description taken in conjunctionwith the accompany ing drawings, in which:

FIG. 1 is a diagram of a driving circuit according to the presentinvention;

FIG. 2 is a diagrammatic plan view, on an enlarged scale, of thetransducer shown in FIG. 1;

FIG. 3A is a wave form explanatory of the condenser voltage;

FIG. 3B is a wave form explanatory of the base-toemitter voltage of thetransistor;

FIG. 3C is a wave form explanatory of the current that flows through thecoil;

FIG. 4 is a diagram of another embodiment of driving circuit embodyingthe present invention;

FIG. 5 is a diagram of still another form of driving circuit embodyingthe present invention; and

FIG. 6 is a diagram of yet another form of driving circuit embodying thepresent invention.

Referring specifically to FIG. 1, there is shown a driving circuitemploying a balance wheel 1 as the output or moving element. The balancewheel together with a coil L, which is electromagnetically coupled withthe balance wheel 1, comprise a transducer which combines the pick-upand driving functions. The balance wheel 1, as better shown in FIG. 2,consists of a rotatably mounted center shaft 2, a disk 3 supported bythe shaft, a permanent magnet 4 fixed to the upper surface of the disk3, and a mass 5 functioning as a counterbalance. The ring-shaped coil Lis secured in position so that when the disk 3 rotates, the magnet 4passes thereunder. The coil L converts an electric signal appliedthereto into a mechanical motion of the balance wheel 1 and, at the sametime, picks up the mechanical motion of the balance wheel 1 and convertsthe same into an electric signal. In other words, it combines bothfunctions of driving and pickup coils. The collector of an NPNtransistor Tr, and the base of a PNP transistor Tr are serially coupledand a resistor R is connected between the base of the transistor Tr, andthe positive terminal of a power source E to bias the transistor Tr, inthe forward direction. To the emitter of the transistor Tr, is connecteda resistor R Between the emitters of the two transistors Tr, and Tr acondenser C is connected for capacitive coupling of the two emitters.The combined pick-up and driving coil L is connected to the emitter ofthe transistor Tr The positive terminal of the power source E, coil L,condenser C, resistor R,, a switch S, and the negative terminal of thepower source E are connected together in a series circuit. The collectorof the transistor Tr is connected to the switch S. Thus, four componentcircuits are formed: i.e., a charge loop consisting of the power sourceE, coil L, condenser C, resistor R and switch S; a discharge loopconsisting of the condenser C, emitter and base of the transistor Tr andcollector and emitter of the transistor Tr a branched discharge loopconsisting of the condenser C, emitter and collector of the transistorTr and resistor R and an oscillating circuit consisting of the powersource E, coil L, emitter and collector of the transistor Tr and theswitch S.

The operation of this driving circuit will now be explained withreference to the graphs of FIG. 3. When the switch S is closed, the baseand emitter of the transistor Tr, are biased in the forward direction,but the transistor Tr, remains in the OFF position because the condenserC is charged by the charge loop.

FIG. 3A gives time t on the axis of abscissa and the voltage V in thecondenser C on the axis of ordinate. By the charge loop, the condenservoltage as represented by a wave form a, is increased up to a certainlevel A,. In FIG. 3B,-time t is plotted on the axis of abscissa againstthe base-to-emitter voltage V of the transistor Tr, on the axis ofordinate. While the condenser C is being charged, the voltage asrepresented by a wave form b rises to the level 8,. The transistor Tr,is switched ON when its base-to-emitter voltage reaches the level 8,.Accordingly, the charge on the condenser C begins to be discharged bythe discharge loop, through the circuit composed of the emitter and baseof the transistor Tr,, collector and emitter of the transistor Tr,, andcondenser C. At the same time, the transistor Tr, is instantaneouslyswitched ON, whereupon a large current flows from the power source Ethrough the coil L and the emitter and collector of transistor Tr On theother hand, the discharge current from the condenser C is also branchedthrough the loop composed of the emitter and collector of the transistorTr,, resistor R, and condenser C. Thereupon, the condenser voltage dropsas represented by a wave form a, in FIG. 3A and the base-to-emittervoltage of the transistor Tr, is increased and maintained by thebranched discharge to a level B in FIG. 3B. The charge on the condenserC is discharged by a time constant which is governed by the capacity ofthe condenser C, the resistance value of the resistor R, and theresistance components of the transistors Tr, and Tr,. When the voltageof the condenser C drops to A the transistor Tr, is switched OFF and thetransistor Tr, is immediately turned OFF, too. FIG. 3C, in which time tis plotted on the axis of abscissa against the current I, that flowsthrough the coil L on the axis of ordinate, shows a driving pulsecurrent e flowing through the coil L. As the transistor Tr, is switchedOFF, the condenser C is charged again, and the cycle of operation abovedescribed is repeated to carry out astable oscillation.

' The period of the astable oscillation is set at a frequency greaterthan the natural frequency of the moving element, and the driving pulsecurrent e,, is set at a value that can give a sufficient driving forceto effect starting of the moving element.

The balance wheel 1 is started by the driving pulse current e,,, and aninducedvoltage is produced in the coil L. Thus, the base-to-emittervoltage of the transistor Tr, is applied with a wave form 17,, or thewave form b shown in FIG. 3B superposed with the in-- duced voltage.With the attainment of the voltage 3,, the transistor Tr, is triggered.At this time the condenser'C is charged as with the wave form a, to avoltage A;,. The transistor Tr, is switched ON with the baseto-emittervoltage 8,, while, in the manner already described, the transistor Tr'is switched ON by the discharge current which is dictated by the timeconstant of the condenser C, with the result that the condenser Cdischarges as represented by the wave form a, and the driving pulsecurrent e, flows through the coil L, .thereby driving the balancewheel 1. As the procedure above described is repeated and the amplitudeof the balance wheel 1v is gradually increased,

the induced voltage also rises and is applied as such to thebase-to-emitter voltage, thus increasing the frequency at which thetransistor Tr, is triggered. Accordingly, the charging and dischargingintervals of the condenser C are shortened by degrees. The pulse widthof the driving pulse current that flows through the coil L while thetransistor Tr is ON is steadily decreased. When the balance wheel 1 hasattained a state of steady vibration with a constant amplitude andfrequency, the pulse current also becomes a stable and steady drivingpulse current e having a predetermined pulse width.

Hence, the balance wheel 1 sustains its steady vibration.

Since the driving pulse current e,, that acts on the vibrator while thevibrator is kept still in the manner above described is much larger thanthe driving pulse current e that acts when the vibrator has attained thestate of steady vibration, the vibrator can start by itself without thenecessity of an external force being applied thereto. When the vibratorattains its steady vibration, the vibrator is driven by a driving pulsecurrent e having a much narrower pulse width than the starting pulsewidths and, accordingly, the power loss is reduced to a minimum. Anotherfeature is that the vibrator is driven with a pulse current that isproduced at a frequency synchronized with the natural frequency of thevibrator.

By relocating the two transistors and coupling the power source with theterminals reversed, it is possible to obtain another embodiment of theinvention. The operation of the resulting driving circuit is entirelythe same as that of the circuit illustrated in FIG. 1.

Another embodiment of the present invention will now be explained withreference to FIG. 4. In this embodiment, a driving circuit having atransducer equipped with a tuning bar 16 instead of the balance wheel 1is used. The tuning bar 16 of the transducer is fixed at one end and isprovided at its free end with a magnet bar 17 attached to one side andwith a mass 18 attached to the other side effective to counterbalancethe weight of the magnet bar. A ring-shaped coil L,,,' is secured inplace such that the magnet bar 17 is slidable with respect thereto. Inthe driving circuit shown, a thermistor Rth is connected between thecollector of the transistor Tr,, and the emitter of the transistor Tr,,.In the figure, reference symbols E,,,, S,,,, R,,, C,,, and R denoteparts similar to their counterparts in FIG. 1. In this embodiment, thetemperature characteristics of the transistors Tr,, and Tr,, can beimproved.

FIG. 5'shows another embodiment of a driving circuit having atransducerin which the moving element is a rotor 29 of a motor. The rotor 29 is aferrite disk mounted on a journalled shaft 30 and has two pairs ofmagnetic poles N and S. A ring-shaped coil L combining the pick-upand'driving functions is fixed in spaced and the positive terminal of apower source E In the diagram, symbols Tr C L S C Tr and R indicateparts which are substantially equivalent to their counterparts in FIG.I. In this embodiment, the driving pulse current can be advantageouslyshaped as desired.

What I claim and desire to Secure By Letters Patent I. A circuit fordriving a moving element comprising: a movably mounted output element,two transistors of opposite polarities, means serially connecting thecollector of one of said transistors to the base of the othertransistor, 21 d-c power source, a biasing resistor connected betweenthe base of said one transistor and said

1. A circuit for driving a moving element comprising: a movably mountedoutput element, two transistors of opposite polarities, means seriallyconnecting the collector of one of said transistors to the base of theother transistor, a d-c power source, a biasing resistor connectedbetween the base of said one transistor and said power source, anotherresistor connected between the emitter of said one transistor and saidpower source, means capacitively coupling together the emitters of saidtransistors, a coil electromagnetically coupled to said output elementand electrically connected to the emitter of said other transistoreffective to both vibrationally drive said output element and pick-upthe movement of the vibrating output element, means connecting thecollector of said other transistor to said power source, and meanselectrically connecting said power source, said other resistor, saidcapacitor and coil in series.